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Old 06-24-2022, 10:28 PM   #1
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watts vs amps on a Vitron multiplus 3000VA 120 amp charger/inverter

Had an interesting conversation with the PO of the new to me Helmsman 38 E. He insists that if there is no load that the inverter uses no power. We had a very small inverter that when you turned it on, the link 20 system reflected that power was being used just being on. He said he turns on the inverter when he leaves the dock and leaves it on 24-7. I looked it up and it says in the brochure that the "Zero Load power is 20 watts". how would I convert that to amps being used if there was no load to the system?
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Old 06-24-2022, 11:02 PM   #2
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Dividing by 12 should get you close, so 1.75A. The main concern is some AC device on the circuits powered by the inverter that gets turned on and you don't know it. A 1 watt load at 120VAC is 10A at 12 VDC so that becomes significant. When ever I have the inverter on I look at the DC load to be sure it is reasonable.

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Old 06-24-2022, 11:03 PM   #3
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Had an interesting conversation with the PO of the new to me Helmsman 38 E. He insists that if there is no load that the inverter uses no power. We had a very small inverter that when you turned it on, the link 20 system reflected that power was being used just being on. He said he turns on the inverter when he leaves the dock and leaves it on 24-7. I looked it up and it says in the brochure that the "Zero Load power is 20 watts". how would I convert that to amps being used if there was no load to the system?

Your understanding is correct, not the PO's. Divide the no-load wattage by the battery voltage (actual, not the nominal 12V or 24V) and you will get the no-load current.
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Old 06-25-2022, 07:41 AM   #4
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Can always verify with a amp meter to see dormant amp draw if any.
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Old 06-25-2022, 07:41 AM   #5
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Your understanding is correct, not the PO's. Divide the no-load wattage by the battery voltage (actual, not the nominal 12V or 24V) and you will get the no-load current.

Thank you. At least I'm not wrong on every single thing as I make the transition from sail to power.
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Old 06-25-2022, 08:38 AM   #6
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One of these Victron meters (or the like) is a very worthwhile investment. A lot of information close at hand. Really tells a story.
Amps, watts, amp hours used, volts, and more.

https://www.amazon.com/Victron-Energ...68428369&psc=1
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Old 06-26-2022, 01:43 AM   #7
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One of these Victron meters (or the like) is a very worthwhile investment. A lot of information close at hand. Really tells a story.
Amps, watts, amp hours used, volts, and more.

https://www.amazon.com/Victron-Energ...68428369&psc=1
the PO partially installed the 702, but he said he didn't need it and so didn't fully install and hook up and program. I deperately want to get it working. I had a link 20 in my Catalina and loved it. a lot of great info.
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Old 06-26-2022, 05:30 AM   #8
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One of these Victron meters (or the like) is a very worthwhile investment. A lot of information close at hand. Really tells a story.
Amps, watts, amp hours used, volts, and more.

https://www.amazon.com/Victron-Energ...68428369&psc=1

There's also the VictronConnect app; it pairs using Bluetooth and then much of the BMV data is available on phone or tablet.

We just got a new pair of batteries for "that" bank and I had to go to the BMV-712 to erase previous history, though.

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Old 06-26-2022, 11:51 AM   #9
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Capran,

I opted to tie my Multiplus and Smart Shunt to the CERBO-GX with Touch 50 display at the helm. That gives me full remote control of the Multiplus as well as showing the AC and DC loads going through the inverter. I don't think the BMV-712 does that. You could also use the Victron Digital Multicontrol, but it doesn't present as much information as the Cerbo.

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Old 06-27-2022, 11:04 AM   #10
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Capran,

I opted to tie my Multiplus and Smart Shunt to the CERBO-GX with Touch 50 display at the helm. That gives me full remote control of the Multiplus as well as showing the AC and DC loads going through the inverter. I don't think the BMV-712 does that. You could also use the Victron Digital Multicontrol, but it doesn't present as much information as the Cerbo.

Tom
The 712 can function with a Cerbo GX the same as a smartshunt, that's the configuration I have on my boat. The 20 watt idle load figure from Victron is conservative, I've seen 3000VA units that are higher than that by double.

To the OP, it sounds like the previous owner knew more than they knew. Getting the monitor hooked up correctly should not be too difficult, Victron's installation guides are pretty good and available online.
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Old 06-27-2022, 11:10 AM   #11
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On the idle draw front, my 2000 VA Multiplus draws pretty close to spec. For the 12v version they spec 9 watts as idle draw, 11 watts for the 24v version (about half of the 3000 VA version). Mine is typically right around 10 watts. Close enough to spec for me.
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Old 07-01-2022, 09:58 PM   #12
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Dividing by 12 should get you close, so 1.75A. The main concern is some AC device on the circuits powered by the inverter that gets turned on and you don't know it. A 1 watt load at 120VAC is 10A at 12 VDC so that becomes significant. When ever I have the inverter on I look at the DC load to be sure it is reasonable.

Tom
A bit of clarification is needed here. Wattage is the product of volts times amps. A one watt load at 120v would be 0.00833 amps, (less than.1A at 12v) not 10 amps. A 1 amp (not watt) draw at 120v is 10A at 12v. If an inverter has a 20W standby demand, that means it draws 1.56 amps at a battery sitting at 12.6v. If you have a 1000ah battery bank and any shore power or solar or wind charging capability, 10-20W is inconsequential. The only thing to worry about is if you have any AC devices plugged in that may cycle on and pull a lot of power. I keep all of the high demand AC circuits turned off when I am off the boat but leave the inverter on so that things like fluorescent engine room lights can be switched on when I return.
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Old 07-02-2022, 06:13 AM   #13
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the PO partially installed the 702, but he said he didn't need it and so didn't fully install and hook up and program. I deperately want to get it working. I had a link 20 in my Catalina and loved it. a lot of great info.

Seeing this and thinking of what you've said in the other thread...

The BMV "install" is mostly just an ethernet plug-in. Could be maybe what your PO didn't do is the "set up" part. Could be all you need to do is tell the thing what parameters you want to see...

I dunno how close your Phoenix MultiPlus is to our newer MultiPlus II, but it seems like it could be ours is very similar to yours and just a generation (or whatever) newer in their model line. (Looks like their current "Phoenix" products are either chargers or inverters, not both.)

In our case, with a BMV-712, we can use the Bluetooth VictronConnect app version to read data -- state of charge, history, etc. -- and some set up commands are available (instead of using the 712 itself) whereas you'd have to use your 702 to do all of that.

But if your PO just didn't choose what to display, doing the setup commands on the 702 will let it display whatever it is you want to see. The setup commands are in the manual.

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Old 07-03-2022, 02:28 PM   #14
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You can reduce idle consumption significantly by using AES. See here for eg
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Old 07-03-2022, 08:15 PM   #15
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The set up for the 702 didn't go as the video we found on line suggested it would but we are getting much needed info. We know that it is NOT hooked up to read the charging amps coming from the charger while hooked to AC on a dock, but it does read incoming amps from the alternator. We're only on night three out, but for each day we have been out it is giving me amps used or charged via motoring, and we have AH currently bring used, total AH used, watts used, percentage of battery left. So far we've been on the move daily and after 20 hours on the hook using 60 to 75 Ah, and the 165 amp ALT. is bringing us to 00 in 1.5 hrs motoring. Noticed unlike the link 20, it does not give a positive number past 00, but that's acceptable. Don't think the 702 has the blue tooth, but even if it did. I wouldn't be able to figure it out. Lol. Feels great to be on the water. But surprised that this boat in a chop is very noisy as water slaps the bottom.
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Old 07-03-2022, 10:44 PM   #16
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The BMV-702 does not have built-in Bluetooth. You need to use a BT dongle (see attached photo).

It sounds like your 702 is fundamentally not installed correctly. It comes with a shunt, and the shunt is to be connected between the battery bank (usually house bank) and the -ve distribution post. And all 12v -ve connections in the boat should be made to that post. This means the alternator, the inverter/charger, the 12V- wire from your MPPT if you have solar, and the 12V distribution panel -ve wiresÖ.everything. Therefore it measures ALL 12V current being taken out of the battery bank, and ALL the 12V current being put back. The 702 then gets connected to that shunt and does itís thing. There is a socket on the back of the meter that accepts a VE.Direct plug. That is where the BT dongle plugs in, and then gives you access to all the info via the Victron Connect app.

Note the above description is for a connection in a boat system that is wired for separate starting and house banks. Not necessary, but if your boat is wired differently you may need to pay much closer attention as to where that shunt goes. Note also the 702 permits monitoring the voltage of a second battery bank. In the above scenario the primary and much more detailed measurements come from the house bank, where load-over-time (ie amp-hours) has some significance, and the secondary connection would be the starting bank, where amp-hours are mostly meaningless.

There is all kinds of documentation on the Victron site for how to install, configure and use this equipment.
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Old 07-04-2022, 12:27 AM   #17
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The Victron inverter likely has a "power saving" search mode as most of them do. If this is enabled, the inverter is shut down, but wakes up once every few seconds and looks for a plugged in AC load. If it sees a load, it will turn on and invert. In these low power modes, they draw very little idle power. There are many reasons why you might not want to enable this (causes problems with some AC loads), and if it is disabled, the idle power of the inverter is significant.
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Old 07-04-2022, 05:42 AM   #18
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Originally Posted by capran View Post
The set up for the 702 didn't go as the video we found on line suggested it would but we are getting much needed info. We know that it is NOT hooked up to read the charging amps coming from the charger while hooked to AC on a dock, but it does read incoming amps from the alternator. We're only on night three out, but for each day we have been out it is giving me amps used or charged via motoring, and we have AH currently bring used, total AH used, watts used, percentage of battery left. So far we've been on the move daily and after 20 hours on the hook using 60 to 75 Ah, and the 165 amp ALT. is bringing us to 00 in 1.5 hrs motoring. Noticed unlike the link 20, it does not give a positive number past 00, but that's acceptable. Don't think the 702 has the blue tooth, but even if it did. I wouldn't be able to figure it out. Lol. Feels great to be on the water. But surprised that this boat in a chop is very noisy as water slaps the bottom.

Hard to imagine how it could be giving you all that other info and NOT charging amps from your charger.

Pardon me; I said earlier the BMV is connected with Ethernet cable... and I meant to say telephone cable. The DMV is connected via ethernet cable.

The Windows wired version of VictronConnect can use their MK3 adapter for USB (to computer) to an ethernet cable (to MultiPlus).

BTW, I just noticed in the DMC manual that the default input current limit is 16... so that may be the simplest reason why yours was set to that.

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Old 07-04-2022, 05:51 PM   #19
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As I said, after 40 years of sailing I am a total newbie. We did spend a full 7 days at the dock with the 702 programmed as it is now and during that time the fridge was on DC mode and it was showing a -250 AH after 2.5 days. Once we learned the fridge did have an AC receptacle and got the AC cord, the DC AH increased only a couple of AH a day. And once we were underway, with 2 hours motoring, the 702 AH decreased steadily until reading 00 AH. I agree you are right, that the PO did not hook it up properly to read the AC dockside charger. My goal is to get through this first cruising season and download the manual and get some help figuring out how to connect it properly
Since we can now use AC power for the fridge while at a dock, and can get the info I need to monitor battery while at anchor (which is a large majority of the time-went to @4 marina nights last year in our sailboat. ) i,ll get by.
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